Bioelectronic medical implants (e.g., stimulators, sensors, communication systems, actuators, etc.) can be useful for monitoring and controlling physiologic function. Making bioelectronic medical implants as small as possible can reduce the invasiveness of such implants and thereby mitigate or eliminate trauma and complications brought about by introducing such implants into a body. Further, non-surgically introducing these implants into the body can reduce the expense of use and make available more applications of use of these implants, permitting increased use of these implants in biomedicine.
Bioelectronic medical implants generally rely on an energy source to electrically power the implants. Typical energy sources can include an implanted battery and/or an external energy transfer system that induces energy into the body. In the latter example, energy can be induced for direct use by the implant and/or to charge an implanted battery. Many existing external energy transfer systems for bioelectronic medical implants use coaxially coupled magnetic induction coils—one internal to a body and one external to the body—forming a transformer. These induction coils are conventionally magnetically coupled because the transparency of the magnetic field can mitigate energy dissipation in the body tissue, resulting in a tolerable generation of heat in the body tissue. For example, a conventional external exciter can include an electrically powered box having a 1-4 centimeter diameter loop inductive coil configured to be electrically powered at radio frequencies in the megahertz region. Meanwhile, a corresponding internal bioelectronic medical implant can have a corresponding loop inductive coil. Accordingly, under the coaxial approach, a magnetic coupling between the coils can induce energy from the external exciter to the internal implant.
The size of the coils can affect and/or define the efficiency with which energy is transferred between the coils. For example, the coupling coefficient of the two coils can depend on the diameters of the coils and the depth of the internal coil in the body. Specifically, because coupling coefficients can decline rapidly, in some cases by the cube of the separation distance of the coils, implanting the internal coil in a body no farther than a distance equivalent to half the diameters of the coils can provide a desirable coupling coefficient of the two coils.
Further, the efficiency of magnetically coupled external energy transfer systems can depend on having two inductor coils coupled by magnetic field lines threading the open areas of the coils. Because the induced electrical energy of the inductor coils is proportional to the loop areas of the inductor coils, using a form factor that has significant length and open width in order to enclose a magnetic path can increase the efficiency of the inductive coupling there between. Thus, it follows that a bioelectronic medical implant using radio frequency magnetic induction can be constrained and/or designed in size and dimension to be equal to the implant inductor loop antenna outer dimension. This in turn can define a size of a surgical opening for implanting a bioelectronic medical implant in a patient's body. Clearly, small entrance wounds are less invasive and/or harmful to the patient's body, yet as mentioned previously, small area inductor loops can be inefficient and present problems of low coupling coefficients that limit functional energy transfer to bioelectronic medical implants when they are placed at depth. Similarly, microwave slot antennas and radiator open lumen loops are coupled primarily to the incident magnetic field.
In addition to electrically powering bioelectronic medical implants, external energy transfer systems can also be used to stimulate bioelectrically excitable tissue. Stimulating bioelectrically excitable tissue can allow the function of the tissue to be manipulated or modified, thus providing a therapeutic or otherwise desirable biological effect. For example, neurostimulation may be used for restoring bodily function in cases of neural injury or disease. Neurostimulation in this context refers to the stimulation of electrically excitable tissues of living things. This can include, for example, the human tissues of the brain, muscle, and/or nervous system.
In practice, electrical currents applied to tissue can affect the membranes of excitable cells of the tissue, causing a depolarizing effect that can lead to a cell action event that depends on its type and biological function. Meanwhile, pulsing electrical currents can fulfill certain physiologic conditions that enable the electricity to be effective.
Applying electrical currents to the body surface can cause the electrical currents to diffuse in the volume conductivity of tissue and attenuate according to well known laws. These electrical currents can also stimulate near-surface nerves and muscle tissues to some degree, but may not be able to reach deeper tissues because of high electrical losses in tissue. Attempting to compensate for these electrical losses may result in raising the current levels high enough to cause electrical shock.
Stimulating bioelectronically excitable tissue can be achieved by applying pulsed electrical currents directly to tissue via surface electrodes at the tissue surface and/or implanted electrodes within the tissue. However, the strong diffusion of electrical current in tissue from surface electrodes means that specific stimulation of a given nerve or nerve fiber within a bundle is very difficult and rather there is a tendency for electrical currents applied to the body surface to broadly stimulate in undesirable ways. Implantable electrodes can overcome these problems, yet like with conventional systems for electrically powering bioelectronic medical implants, are typically invasive and conventionally are supplied energy by wires running through the skin and/or bulky implanted energy sources, such as, for example, a battery and/or an inductor coil of an external radio frequency energy transfer system.
For example, like for conventional systems for electrically powering bioelectronic medical devices, electrical currents can be delivered to tissues by way of radio frequency induction to a bioelectronic medical implant. These systems typically use an inductor implanted within the body to magnetically couple to an external radio frequency field. However, these implants are generally relatively large and can be on the order of a centimeter in size.
Despite the use of magnetically coupled external energy transfer systems, capacitively coupled (i.e., electric field coupled) external energy transfer systems have largely been ignored and have been considered ineffective for powering bioelectronic medical implants and/or stimulating bioelectrically excitable tissue.
Meanwhile, having identified numerous drawbacks associated with magnetically coupled external energy transfer systems, a need or potential for benefit exists for a system for electrically powering a bioelectronic medical device and/or for stimulating bioelectrically excitable tissue that allows for non-invasive implantation, at depths in the biological tissue that are large relative to the implant cross-sectional area, without sacrificing functional energy transfer to the implanted device to a point that a desired level of stimulation cannot be met.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically and/or otherwise. Two or more electrical elements may be electrically coupled but not be mechanically or otherwise coupled; two or more mechanical elements may be mechanically coupled, but not be electrically or otherwise coupled; two or more electrical elements may be mechanically coupled, but not be electrically or otherwise coupled. Coupling may be for any length of time, e.g., permanent or semi-permanent or only for an instant.
“Electrical coupling” and the like should be broadly understood and include coupling involving any electrical signal, whether a power signal, a data signal, and/or other types or combinations of electrical signals. “Mechanical coupling” and the like should be broadly understood and include mechanical coupling of all types.
The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.